The present invention relates generally to automatically repositioning fifth wheel hitches for use with fifth wheel trailers and towing vehicles, and particularly to fifth wheel hitches that automatically reposition the pivot point of the hitch rearward as the towing vehicle turns relative to the trailer by utilizing a rotational pivotable mechanism with four links.
The background information discussed below is presented to better illustrate the novelty and usefulness of the present invention. This background information is not admitted prior art. The following discussions of related art are provided as illustrative and exemplary of problems now present in the art.
Fifth wheel trailers and tow vehicles for fifth wheel trailers are generally well known in the art. Fifth wheel trailers are usually much longer and heavier than tent campers and travel trailers. Thus a fifth wheel trailer typically requires a tow vehicle, such as a pickup truck. The front portion of a fifth wheel trailer generally extends over the rear portion of the tow vehicle so that a portion of the trailer's weight is carried directly over the rear axle of the tow vehicle. To accommodate the weight of the trailer a special hitch assembly is required. Trailers are fitted with a hitch box which includes a support plate and a downwardly extending hitch pin. Tow vehicles are fitted with a base plate having an aperture and a latch mechanism for mounting, and securing the trailer to the tow vehicle. In presently available hitch assemblies the support plate, which is where the mechanism's single pivot point is located, rotates relative to the base plate about the hitch pin. Typically, the hitch assembly, and thus, the single vertical pivot axis, is mounted directly over or a short distance in front of the rear axle of the tow vehicle in order to maintain proper weight distribution.
To prevent contact between a trailer and a cab while maneuvering in tight spaces, the clearance between the pivot point and the rear of the cab must be at least half the width of the trailer. Trailers come in a variety of widths and lengths from long tractor trailers to short mini-trailers. Recreational trailers, for example, are often as much as 102 inches wide, but more typically are 96 inches and can be less. Such a recreational vehicle if routinely towed by a short bed pickup truck. Most short bed pickups have a bed that is typically only about 6 feet long. Beds that are 8 feet long are available on regular and extended cabs, as are short beds. Although the shorter bed pickups have the towing capacity to handle fifth wheel trailers, they do not have enough clearance between the axle and the rear of the cab to allow the trailer to pivot a 90 degree angle without the trailer coming into contact with the cab and potentially causing damage to the truck and injury to occupants. Generally, a fifth wheel trailer contacts the cab of a short bed pickup at angles much less than 90 degrees.
A number of attempts have been made to adapt fifth wheel trailers for towing by such short bed trucks, but each of these has been shown to have a significant drawback. One attempt uses a hydraulically operated sliding base to move the hitch assembly, and hence the pivot point, rearward from the cab. This assembly is likely to be expensive, difficult to maintain, and has to be driver actuated, which means the vehicle with trailer must be at rest at some safe spot off of the road. Actuating the working mechanism of this assembly requires a delay or lag time, which would mean that during an accident, such as a jackknife, the system would operate too slowly to prevent the trailer from contacting and most likely damaging the cab.
Another approach, employs a sliding base to move the pivot point from a front position to a rear position and requires the operator to exit the truck to manually release the locking mechanism, lock the brakes on the trailer, and then reenter the truck to drive it forward until the desired rearward position of the pivot point is reached before the trailer is able to pivot, relative to the truck, without making an undesirable contact with the cab. When preparing to drive the truck/trailer combination at highway speeds, the process is reversed to move the hitch to the forward position. While this method solves the clearance problem, it requires the operator to anticipate when sharp turns were going to be made in order to move the hitch before the fact. This system also could create a hazard if tight turns were required in a traffic situation and thus would be practically useless in an emergency.
Yet still another attempt, offers a sliding hitch assembly that automatically moves rearward away from the truck cab in response to pivotal movement of the trailer and the truck that typically occurs during normal driving. The sliding hitch assembly includes a sliding base plate, mounted on a pair or rods. An additional plate is attached to the hitch box of the trailer, with a key that prevents rotation between the hitch box and base plate. A lever arm extends from the base plate, and a cam follower attached to the end of the lever arm engages a stationary slot that extends substantially perpendicular to the rods. As the truck turns relative to the trailer, the rotation of the base plate causes the cam follower to move within the slot towards one of the slot ends, which in turn causes the base plate to slide back and forth along the rods. As the base plate is rotated the base plate moves between a forward position, in which the cam follower is at the center of the slot, and a rearward position, in which the cam follower is near one of the slot ends. When in the forward position, the hitch pin receiving aperture, and thus the pivot point of the trailer, is directly or slightly in front of the axle centerline. As the base plate rotates relative to the truck, the lever arm mechanism causes the base plate to slide rearwardly on the rods, moving the pivot point of the trailer away from the rear of the truck cab. The numerous components of this single pivot point device tend to make this device more prone to breakage, more costly to repair, and cause the device to be relatively expensive.
It is clear then that, there still exists a need for a hitch assembly that allows fifth wheel trailers to be towed without the fear of contact between the trailer and the truck where the hitch assembly provides for automatic repositioning of the effective pivot point in response to pivoting movement between the trailer and the towing vehicle and that does not require the expense, maintenance, and lag time of hydraulic systems, and that does not require the operator to exit the vehicle in order to lock or unlock the hitch assembly.